from turtle import *
from random import *
from math import *

def tree(n, l):
    pd() # 下笔
    # 阴影效果
    t = cos(radians(heading() + 45)) / 8 + 0.25
    pencolor(t, t, t)
    pensize(n / 3)
    forward(l) # 画树枝


    if n > 0:
        b = random() * 15 + 10 # 右分支偏转角度
        c = random() * 15 + 10 # 左分支偏转角度
        d = l * (random() * 0.25 + 0.7) # 下一个分支的长度
        # 右转一定角度，画右分支
        right(b)
        tree(n - 1, d)
        # 左转一定角度，画左分支
        left(b + c)
        tree(n - 1, d)

        # 转回来
        right(c)
    else:
        # 画叶子
        right(90)
        n = cos(radians(heading() - 45)) / 4 + 0.5
        pencolor(n, n*0.8, n*0.8)
        circle(3)
        left(90)

        # 添加0.3倍的飘落叶子
        if(random() > 0.7):
            pu()
            # 飘落
            t = heading()
            an = -40 + random()*40
            setheading(an)
            dis = int(800*random()*0.5 + 400*random()*0.3 + 200*random()*0.2)
            forward(dis)
            setheading(t)


            # 画叶子
            pd()
            right(90)
            n = cos(radians(heading() - 45)) / 4 + 0.5
            pencolor(n*0.5+0.5, 0.4+n*0.4, 0.4+n*0.4)
            circle(2)
            left(90)
            pu()

            #返回
            t = heading()
            setheading(an)
            backward(dis)
            setheading(t)

    pu()
    backward(l)# 退回

bgcolor(0.5, 0.5, 0.5) # 背景色
ht() # 隐藏turtle
speed(0) # 速度，1-10渐进，0最快
tracer(0, 0)
pu() # 抬笔
backward(100)
left(90) # 左转90度
pu() # 抬笔
backward(300) # 后退300
tree(12, 100) # 递归7层
done()